The present invention relates to a digital communication system, which can perform a highly reliable digital communication at low cost by digital modulation after a packet process and an 8 bit-14 bit encoding (EFM) process for desired data at a transmission station.
Conventionally, a karaoke performing apparatus has means for transferring a song data read out from an optical disc such as a CD (compact disc), as shown in FIG. 2 (for example, see Unexamined Japanese Patent Publication No. 5-119788). Specifically, double phase shift keying (2 PSK) modulation is performed at an RF modulator 2 according to EFIM data, such as, karaoke performance data, which is reproduced from a CD player 1, and the modulated output is transmitted to an RF demodulator 4 via a transmission cable 3. At the demodulator 4, the transmitted output is demodulated to pick up therefrom the EFM data, which is then supplied to an EFM decoder 5. At the decoder 5, the EFM data is decoded, and the decoded data is supplied to a D/A converter 6. An analog signal from the converter 6 is supplied to a sound system 8 along with a singing voice signal from a microphone 7 so as to generate mixed sounds.
According to the foregoing data transfer system, since the digital transmission system and an error correction process is performed at the EFM decoder 5 and the like, the highly reliable data transmission is possible as compared with an analog transmission system. However, there is inconvenience that recorded data can be transmitted in only one way. On the other hand, as a further highly reliable digital communication system than that shown in FIG. 2, a system of quadruplex PSK (4 PSK) modulation type is used in a satellite broadcast (BS), which, however, is inconvenient in that encoding for modulations is complicated, leading to high cost.